Flagella of Chlamydomonas resemble the cilia of sensory cells and possibly the cilia of embryonic cells in their ability to detect and transmit information. Specifically, they signal the occurance of sexual, lectin and antibody-mediated agglutination; they appear to be involved in phototactic orientation; and they change their length in response to changes in the cell cycle and the external environment. Our objective is to ascertain to what extent the capacity of the flagella surface to move attached ligands (e.g. polystyrene beads or antibody) is functionally related to its signalling capacity. To this end, one series of experiments is designed to define more precisely the parameters involved in signalling and surface-motility phenomena, using proteolytic enzymes, lectins, antisera, antimitotic drugs, and mutant strains as specific probes. The second series of experiments is designed to identify and characterize flagellar membrane polypeptides that are potential candidates as sensory-modulation components and/or as components of the surface-motility apparatus, using 125I-surface labeling, SDS gel electrophoresis, and peptide mapping as probes. The third series of experiments will analyze the properties of glycosylated flagellar membrane tubulins which give evidence of functioning in both signalling and surface motility.